1. Field of the Invention
The present invention relates to methods for manufacturing substrates for flat panel displays and relates to methods for forming barrier ribs in flat panel displays. The present invention particularly relates to a method for manufacturing a substrate for flat panel displays such as plasma display panels (PDP), plasma addressing liquid crystal display panels (PALC), and field emission display panels (FED), which include partition walls for partitioning a space between a pair of float glass substrates and relates to a method for forming such barrier ribs in such flat panel displays.
2. Description of the Related Art
An exemplary conventional method for forming a rear substrate for plasma display panels is described below. FIGS. 1A through 10E are an illustration showing steps in a conventional method for forming barrier ribs. As shown in FIG. 1A, in a first step, address electrodes 11 are formed on the top surface (non tin-side surface) of a float glass substrate 10. When the address electrodes 11 are of a thin film technology, the address electrodes 11 are formed according to the following procedure: a layer consisting of a first chromium sub-layer, a copper sub-layer, and a second chromium sub-layer disposed in that order is formed by a sputtering process, and the formed layer is then etched by a photolithographic process so as to form a predetermined pattern. When the address electrodes 11 are of a thick film technology, the address electrodes 11 are formed according to the following procedure: silver powder, a glass binder, a resin, a solvent, and the like are mixed to prepare silver paste, and a pattern is formed by a screen-printing process using the silver paste. In this step, the address electrodes 11 are formed on the top surface (non tin-side surface) of the float glass substrate in order to prevent the following phenomenon: when the address electrodes 11 are formed on the bottom surface (tin-side surface) of the float glass substrate, copper and silver react with tin lying on the bottom surface to form colloid containing copper and silver, and the formed colloid are diffused in the float glass substrate, thereby causing colored portions in the float glass substrate. Dielectric paste is then applied onto the address electrodes 11, and the resulting dielectric paste is dried and then fired to form a dielectric layer 12.
In a second step shown in FIG. 1B, a partition wall paste 13 is applied over the dielectric layer 12 formed in the first step, and the resulting partition wall paste 13 is then dried. The partition wall paste 13 may be applied onto the dielectric layer 12 with a dye coater in one step. Alternatively, the partition wall paste 13 may be provided on the dielectric layer 12 by a screen-printing process to form a plurality of layers.
In a third step shown in FIG. 1C, after the partition wall paste 13 is dried, resist pattern portions 14 are provided on the partition wall paste 13 such that the resist pattern portions 14 cover regions for forming barrier ribs. The resist pattern portions 14 are usually formed according to the following procedure: a dry resist film is joined to the partition wall paste 13, and the resulting dry resist film is then etched by a photolithographic process so as to form a desired pattern.
In a fourth step shown in FIG. 1D, the partition wall paste 13 is sandblasted with a sandblast gun 15 using an abrasive 16 containing fine calcium particles, thereby removing portions of the partition wall paste 13, the portions not being covered with the resist pattern portion 14.
In a fifth step shown in FIG. 1E, the resist pattern portions 14 are removed from the resulting partition wall paste 13, and the partition wall paste 13 is then fired to form barrier ribs 17.
In the float glass substrate 10 having the above components formed according to the above procedure, grooves are disposed between the barrier ribs 17. Fluorescent layers having the corresponding three primary colors are then formed in the corresponding grooves. Another substrate is separately prepared. A plurality of pairs of sustaining electrodes, a transparent dielectric layer covering the sustaining electrodes, and a protective layer comprising MgO and the like and covering the transparent dielectric layer are formed on the substrate. The substrate is joined to the float glass substrate 10 in such a manner that all the components are disposed between the substrates. A sealing material is provided at the periphery of the joined substrates to seal the space therebetween, and gas is evacuated from the space. The space is then filled with a mixture gas containing neon and xenon, thereby obtaining a plasma display panel.
In order to reduce the cost of manufacturing plasma display panels, the inventors have proposed a new method for forming barrier ribs, and the method is disclosed in Japanese Unexamined Patent Application Publication No. 2001-43793.
In the above method, grooves arranged at a predetermined pitch are directly provided in a surface of a rear substrate processed in a step of manufacturing a plasma display panel to form barrier ribs.
FIG. 2 is an illustration showing a method for manufacturing a glass substrate (float glass substrate) by a float process. As shown in FIG. 2, raw materials such as silica sand, soda ash, and limestone are supplied to a raw material inlet port 108 placed on the left side of a melting furnace 101 and are then melted at 1,600° C. to form base glass. The base glass is allowed to move in the melting furnace 101 in the right direction in the figure while the base glass releases bubbles contained therein.
The base glass moved from the melting furnace 101 is sent to a float bath 102 containing molten tin 104 having a surface that is flat due to gravity. The base glass is formed into a float glass plate 106 having a predetermined thickness in the float bath 102. A surface of the float glass plate 106 is in contact with the molten tin 104 in this step. This surface is called a bottom surface (tin-side surface) and the back of this surface is called a top surface (non tin-side surface). The float glass plate 106 contains tin at the periphery of the bottom surface.
The float glass plate 106 moved from the float bath 102 is sent to an annealing furnace 103 and is then annealed therein in order to remove permanent strain from the float glass plate 106 while the float glass plate 106 moves on rollers 105. After the float glass plate 106 is moved from the annealing furnace 103, the float glass plate 106 is cut into float glass substrates having a predetermined size at a cutting portion 107.
In each float glass substrate manufactured by this float process, large bubbles are removed from the base glass in the melting furnace 101. However, small bubbles having a diameter of about several hundred μm or less remain at the periphery of the top surface of the base glass, which is then solidified. Thus, the float glass substrate has small bubbles at the periphery of the top surface.
In conventional methods for manufacturing barrier ribs, the bubbles remaining in the float glass substrate do not cause problems because address electrodes, a dielectric layer, and the barrier ribs are formed on the float glass substrate.
However, in a method for directly forming barrier ribs in the float glass substrate by a subtractive process, the small bubbles remaining at the periphery of the top surface (non tin-side surface) of the float glass substrate cause the following defects in the barrier ribs when grooves are formed in the top surface: the grooves have a depth larger than a desired value in proportion to the size and number of the bubbles when the bubbles lie at the groove bottom, and the barrier ribs have holes extending therethrough when the bubbles lie in regions for forming the barrier ribs.
In order to solve the above problems, the inventors have researched defects in barrier ribs formed in the top surface of float glass substrates in detail, and found that such defects are caused by bubbles remaining at the periphery of the top surface of each float glass substrate. As a result, the inventors have made this invention in which grooves are formed in the bottom surface (tin-side surface) of the float glass substrate by a subtractive process to form barrier ribs for flat panel displays.